How to close a Java Swing application from the code

Your JFrame default close action can be set to "DISPOSE_ON_CLOSE" instead of EXIT_ON_CLOSE (why people keep using EXIT_ON_CLOSE is beyond me).

If you have any undisposed windows or non-daemon threads, your application will not terminate. This should be considered a error (and solving it with System.exit is a very bad idea).

The most common culprits are java.util.Timer and a custom Thread you've created. Both should be set to daemon or must be explicitly killed.

If you want to check for all active frames, you can use Frame.getFrames(). If all Windows/Frames are disposed of, then use a debugger to check for any non-daemon threads that are still running.

I guess a EXIT_ON_CLOSE

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

before System.exit(0) is better since you can write a Window Listener to make some cleaning operations before actually leaving the app.

That window listener allows you to defined:

public void windowClosing(WindowEvent e) {
    displayMessage("WindowListener method called: windowClosing.");
    //A pause so user can see the message before
    //the window actually closes.
    ActionListener task = new ActionListener() {
        boolean alreadyDisposed = false;
        public void actionPerformed(ActionEvent e) {
            if (frame.isDisplayable()) {
                alreadyDisposed = true;
                frame.dispose();
            }
        }
    };
    Timer timer = new Timer(500, task); //fire every half second
    timer.setInitialDelay(2000);        //first delay 2 seconds
    timer.setRepeats(false);
    timer.start();
}

public void windowClosed(WindowEvent e) {
    //This will only be seen on standard output.
    displayMessage("WindowListener method called: windowClosed.");
}

Try:

System.exit(0);

Crude, but effective.

If I understand you correctly you want to close the application even if the user did not click on the close button. You will need to register WindowEvents maybe with addWindowListener() or enableEvents() whichever suits your needs better.

You can then invoke the event with a call to processWindowEvent(). Here is a sample code that will create a JFrame, wait 5 seconds and close the JFrame without user interaction.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class ClosingFrame extends JFrame implements WindowListener{

public ClosingFrame(){
    super("A Frame");
    setSize(400, 400);
            //in case the user closes the window
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setVisible(true);
            //enables Window Events on this Component
            this.addWindowListener(this);

            //start a timer
    Thread t = new Timer();
            t.start();
    }

public void windowOpened(WindowEvent e){}
public void windowClosing(WindowEvent e){}

    //the event that we are interested in
public void windowClosed(WindowEvent e){
    System.exit(0);
}

public void windowIconified(WindowEvent e){}
public void windowDeiconified(WindowEvent e){}
public void windowActivated(WindowEvent e){}
public void windowDeactivated(WindowEvent e){}

    //a simple timer 
    class Timer extends Thread{
           int time = 10;
           public void run(){
     while(time-- > 0){
       System.out.println("Still Waiting:" + time);
               try{
                 sleep(500);                     
               }catch(InterruptedException e){}
             }
             System.out.println("About to close");
    //close the frame
            ClosingFrame.this.processWindowEvent(
                 new WindowEvent(
                       ClosingFrame.this, WindowEvent.WINDOW_CLOSED));
           }
    }

    //instantiate the Frame
public static void main(String args[]){
          new ClosingFrame();
    }

}

As you can see, the processWindowEvent() method causes the WindowClosed event to be fired where you have an oportunity to do some clean up code if you require before closing the application.

I think, the idea is here the WindowListener - you can add any code there that you'd like to run before the thing shuts down